1. Field of the Invention
The present invention relates to chemical methods to esterify xanthophylls obtained from diverse sources including marigold flowers and red peppers.
2. Description of the Related Art
During several decades xanthophylls have been subjected to constant research due to their use both in human and animal consumption. In the poultry business the color of the egg yolk as well as that of the broilers skin is an important factor related to quality and consumer preference. It is because of this that there is a constant effort to provide poultry formulations including better pigmenting agents where their physical and chemical characteristics allow a better absorption thus rendering optimal pigmentation at lower costs.
Xanthopylls in marigolds are esterified mainly with palmitic, stearic and myristic acids and others of less importance (Alam et al. (1968) Lipids 3(2): 183–184). Egg laying hens make better use of lutein esters than the crystalline form of free lutein (Philip et al. (1976) J. Food Sci. 41:23–25) indicating that it could be due to a better solubility of the esters in lipids. Similar results were reported in the absorption of capsanthin from red peppers (Hamilton et al. (1990), Poult. Sci 69: 462–470). It was found that free lutein was better absorbed by broilers than the esters (Fletcher et al. (1986) Poult. Sci. 65: 1708–1714). Tyczkowski and Hamilton (1986) demonstrated that lutein is found free in the blood serum of broilers and that it is deposited in the skin as an ester after enzymatic transformation. Differences were observed between the polar interactions derived from the esterified and free forms of zeaxanthin and some of their rheological consequences (Zsako, et al. (1987) Rev. Roum. Chim. 32: 739–748). As the carbon chain that forms the fatty acid of the carotenoid ester is shorter, there is less steric hindrance and greater polarity. Regarding the relative polarity of several carotenoids, the allylic hydroxy is up to 50% more polar than the acetyl group thus conferring zeaxanthin a higher polarity than lutein and also lutein being more polar than the acetylated derivatives of zeaxanthin or lutein (Krinsky (1963) An. Biochem. 6: 293–302). The digestibility of the fatty acids in broilers as well as layers is inversely related to the length of the carbon chain (Yoshida, et al. (1970) Agr. Biol. Chem. 34(11): 1668–1675). Those with better bioavailability have between 5 to 12 carbons and those with lower bioavailability have less than 5 carbons (except acetic acid) or more than 12 carbons. A similar relation applies for the esters indicating that methyl, ethyl, propyl, butyl, amyl and hexyl derivatives of the fatty acids mentioned above are better absorbed by both broilers and layers. The studies by Tyczkowski and Hamilton indicate that the length of the carbon chain, and the saturation and concentration of the lipids included in the poultry diets notably influence the lutein absorption. A better uptake is observed when the fatty acids are of short chain and/or unsaturated.
The above is explained based on the micellar theory of digestion and the polarity of the oxycarotenoids. In broilers it has been demonstrated that lutein, zeaxanthin and other carotenoids are better absorbed in their free form than as natural esters like palmitate, stearate, myristate, etc, having a definite effect in skin pigmentation. In broilers, lutein from marigolds is hydrolyzed before absorption in the intestine and transported in this form to different tissues, but before deposition in the skin the pigment is re-esterified (Martin-Garmendia et al. (1981) Comp. Biochem. Physiol. 70a: 619–621). It is important to mention that the esterified xanthophylls have a better stability against several adverse physical and chemical factors than their equivalent hydrolyzed forms. Breivik, et al. (WO 03/003848A1) describe the use of a diester of astaxanthin prepared with an omega-3 fatty acid and/or a short chain carboxylic acid for enhancing the growth of farmed fish.
Traditionally esterification of marigold carotenoids is carried out for analytical purposes by making acetylated derivatives or partially acetylated derivatives by reacting the carotenoid with acetic anhydride in the presence of pyridine (Eugster (1995) Carotenoids: Vol. 1A, G. Britton, ed. page 74, Birkhauser; Molnar (2002) Helv. Chim. Acta 85:2349).
Bernhard, et al. (U.S. Pat. No. 4,883,887) developed several intermediates for the synthesis of the same carotenoids among which are mentioned their mono and diacetylated derivatives using for this process acetic anhydride at a very low temperature.
Torres Cardona et al. (U.S. Pat. No. 5,523,494), describe a process for esterification of marigold xanthophylls using acetic or propionic anhydride obtaining the corresponding acetate or propionate of the carotenoid. The presence of water in the reaction medium makes handling of the reaction difficult due to the violent reaction of the anhydride. This situation favors intensive degradation of the pigments and the accumulation of acetic or propionic acid as well as their respective salts.
Others have reported processes for esterification of carotenoids using chlorides of fatty acids which are needed to bind to the chain. No process has been reported for commercial purposes in which acetic anhydride or acid chlorides have not been used in some way or another for the esterification of marigold xanthophylls.